Pen



FIG. 1 is a lower front right perspective view of a pen showing my new design;

FIG. 2 is a front elevation view thereof, with the rear elevation view being a mirror image of the front elevation view;

FIG. 3 is a right side elevation view thereof, with the left side elevation view being a mirror image of the right side elevation view;

FIG. 4 is an enlarged top plan view thereof; and,

FIG. 5 is an enlarged bottom plan view thereof. 

The ornamental design for a pen, as shown and described. 